Operate one-setting taxiway lights during the day when ___.

• A. the pilot calls for departure clearance
• B. the pilot calls for taxi instructions
• C. visibility is less than 3 miles
• D. visibility is less than 1 mile

Answer: (D)

Guiding aircraft on the ground in reduced visibility is the purpose of daytime taxiway lighting. When prevailing visibility drops to less than a mile, the airport should operate the taxiway lights at a single, low intensity setting. This level provides enough contrast to help pilots identify taxiway edges and centerlines without causing glare in bright daylight, improving safe taxi operations when visibility is poor. The other situations listed—pilot requests for clearance or taxi instructions—aren’t about lighting control, and visibility conditions like 3 miles or 1 mile alone don’t define the required daytime lighting setting beyond this specific threshold.